1. Technical Field
The present invention relates to an oscillation circuit, an oscillator, a method of manufacturing an oscillator, an electronic device, and a moving object.
2. Related Art
In a resonator such as a quartz crystal resonator (piezoelectric resonator) or a micro electro mechanical systems (MEMS) resonator, characteristics of the resonator are inspected by performing an overdrive inspection in which an alternating current (AC) signal of a high current, voltage, or power is applied and the resonator is driven to thereby inspect frequency characteristics of the resonator, a drive level inspection in which a signal obtained by increasing and decreasing an AC signal of a high current, voltage, or power is applied in a stepwise manner and the resonator is driven to thereby inspect the fluctuation of frequency characteristics of the resonator, or the like.
On the other hand, the development has been performed of an oscillator in which a quartz crystal resonator and an oscillation circuit are accommodated in the same accommodation container, in order to achieve a reduction in the size of the oscillator. For this reason, various devices have been performed in order to inspect characteristics of a resonator after the quartz crystal resonator and the oscillation circuit are mounted within the same accommodation container.
JP-A-2009-201097 discloses a quartz crystal oscillator capable of being miniaturized by causing a functional terminal of an oscillator to double as an inspection terminal of a quartz crystal resonator, as compared with a case where an inspection terminal is independently provided.
However, in the quartz crystal oscillator disclosed in JP-A-2009-201097, a high voltage may be applied to both ends of a variable capacitive element embedded in an oscillation circuit, for example, during an overdrive inspection or a drive level inspection, which results in a concern that the variable capacitive element may be damaged. In particular, in an oscillator in which a frequency changes depending on a control voltage, a variable capacitive element may be realized using an MOS having a thin gate oxide film or a small size L in order to increase a voltage sensitivity of a frequency (the amount of change in a frequency with respect to the amount of change in a control voltage). Such a variable capacitive element has a low withstand pressure, and thus there is a higher tendency for the element to be damaged when a high voltage is applied to the both ends thereof. Alternatively, a service time of a product may be decreased. This problem is not limited to the variable capacitive element and similarly occurs also in a capacitive element having a fixed capacitance value or various types of electronic elements such as an inductor.